Hydrosilylation reactions involve the addition of an Si-H across a terminal olefinic double bond. They have been conducted historically using catalysts derived from chloroplatinic acid (CPA), although elemental platinum on various supports has also been used. These reactions typically suffer from side reactions such as dehydrocondensation, and in the case of certain polyethers, acetal formation.
Dehydrocondensation initially involves the reaction of a hydridosilicon compound and a hydroxyl-containing material such as an alcohol or water to yield hydrogen and an alkoxy silane or silanol. The alkoxy silane may form a crosslinked material in a subsequent reaction step, and the silanol may also subsequently form crosslinked material under the reaction conditions.
Acetal formation occurs when an allyl polyether starting material undergoes molecular rearrangement to a propenyl ether which reacts with alcohol present in the system.
Other difficulties which have been experienced in chloroplatinic acid catalyzed hydrosilylation reactions are: a requirement for relatively high platinum levels in the reactions, with the attendant expense; insufficiently high rates of hydrosilylation; a requirement for relatively high reaction temperatures, with the attendant risk of increasing objectionable side reactions; and objectionable selectivity of the hydrosilylation reaction, with some olefinic materials in the reaction mixtures reacting in preference to others.
Traditionally, polysiloxane-polyether copolymer surfactants have been prepared by a hydrosilylation reaction between a polysiloxane containing Si-H moieties and a terminally unsaturated polyether, in a solvent such as toluene or isopropanol. These solvents must ultimately be removed from the reaction product in the manufacturing process, leading to environmental and economic difficulties. The use of isopropanol also suffers from the additional difficulties that a buffer is required to prevent or reduce dehydrocondensation between Si-H moieties and the alcohol, relatively high platinum levels are required, and the hydrosilylation reactions do not always occur as rapidly as desired.
To avoid the above-discussed problems associated with the use of solvents in the hydrosilylation reaction for preparation of siloxane-polyether copolymers, it has been proposed to conduct the reaction under solvent-less conditions When this was first attempted, high yields of dehydrocondensation products and acetals were produced, ultimately giving extensive crosslinking. Addition of alkali metal carboxylate salts to the system controlled the dehydrocondensation and acetal-forming reactions, as shown in U.S. Pat. No. 4,847,398, but resulted in hydrosilylation reactions which in some cases exhibited objectionable selectivity, low reaction rates, and high platinum requirements.
In addition to polysiloxane-polyether copolymer surfactants, certain silane materials are also prepared via hydrosilylation reactions. Such reactions typically involve a silane material such as trichlorosilane or a trialkoxysilane, and an olefinically-unsaturated material such as allyl chloride. These reactions are sometimes hard to initiate, requiring high reaction temperatures which can produce reduced selectivity and objectionable increases in undesired byproducts of the reaction.
Certain amines have been employed in hydrosilylation reactions to control the dehydrocondensation and acetal-forming side reactions. These have been relatively simple nonhindered amines. In some cases they have had an inhibiting effect on the rate of the hydrosilylation reaction. The prior art has apparently not recognized the distinction between amines and phosphines which can act as bases toward proton donors and also act as general nucleophiles or ligands for the platinum catalyst, and the highly hindered amines and phosphines which cannot act as nucleophiles or ligands for the platinum catalyst
Treatment of chldroplatinic acid with an aminofunctional silane or siloxane is described in U.S. Pat. No. 3,795,656. The resulting catalysts are described in U.S. Pat. No. 4,398,010 as being too slow to react for certain applications, and this patent further discloses reacting the initially formed ammonium-platinum complex with a compound having aliphatic unsaturation in the presence of a basic compound to form a platinum complex having improved hydrosilylation activity.
The use of compounds containing phosphorus, sulfur, nitrogen, or aliphatic unsaturation to suppress platinum catalyzed reaction of water or OH groups with excess SiH groups to generate hydrogen in cured addition-type silicone material is disclosed in U.S. Pat. No. 4,605,722. Some of these materials are considered inhibitors or poisons for general hydrosilylation reactions. Examples of nitrogen- and phosphorous-containing compounds employed by the reference are N,N-diethylaninoethanol, and triethylphosphine.
Ligands containing both phosphine and amine functionalities have been described for use with various transition metals for hydrosilylation of aliphatic olefins. See Chemical Abstracts 109: 54927v.
Hydrosilylation of allyl chloride with trichlorosilane catalyzed by platinum on charcoal or chloroplatinic acid gives substantial amounts of silicon tetrachloride and n-propyltrichlorosilane byproducts. See U.S. Pat. No. 2,637,738 and Ryan, et al., J. Am. Chem. Soc., 82, 3601 (1960), respectively. Diarylamines such as diphenyl amine and N,N'-diphenyl-p-phenylenediamine have been shown to function as promoters for the reaction between trichlorosilane and allyl chloride See U.S. Pat. No. 3,925,434. Unbranched tertiary amines such as tributylamine have also been used for the reaction between allyl chloride and trichlorosilane. See German Pat. No. 1,156,073. Other examples of the use of unbranched tertiary alkyl and mixed alkyl/aryl amines have been described in Chemical Abstract 111:78085m.
It would be desirable to have improved promoters for platinum-catalyzed hydrosilylation reactions, to provide advantages such as faster reactions, reduced side reactions, lower Pt usage, and/or superior product yields and quality. Such promoters are the subject of the present invention.